Blood pressure control by efferent (sympathetic nerve activity) and afferent (baroreflex) pathways develops postnatally in rats in a timed sequence i.e., SNS ganglionic transmission day 6-7, baroreflex day 12-14. The long term objective is to see if perturbations of developmental sequence in neonates leads to disturbance of blood pressure control which persist into or appear in maturity. In this in vivo project experimentally induced perturbations are analyzed physiologically and ultrastructurally in a simple SNS pathway to smooth muscle, cervical innervation of levator palpebrae muscle (LPM) in which measurements can be made from pre-, postganglionic and end organ components and data used to aid interpretation of effects in the more complex SNS vasomotor pathway in which only an indirect index of endorgan function, blood pressure, can be assessed in the neonate. In normotensive rats, (Sprague-Dawley) interventions are tested w ich affect onset time and/or level of SNS activity reaching endorgans. Onset of SNS activity via ganglionic synaptogenesis is accelerated (postnatal thyroid hormone), retarded (propylthiouracil thypthyroidism) and prevented (cervical preganglionic denervation). Level of SNS activity is enhanced with normal onset time (6-7 days, prenatal reserpine) or accelerated onset (2 days, prenatal reserpine + postnatal T3) and the effect on developoment of SNS activity of preventing development of baroreflex is tested (denervate sinoaortic receptors shortly after birth). We measure pre-and postganglionic impulses (CNS output and ganglion transmission), LPM contraction and BP response to tyramine (postganglionic nerve terminal function) and to NE (LPM and vascular muscle reactivity) and make quantitative and morphometric ultrastructural observations on ganglion, post-ganglionic neuron and endorgan (LPM and mesenteric vessels). WKY and WHY-spontaneously hypertensive (SHR) rats are compared to Sprague-dawley to see if there are spontaneous abnormalities in neonatal development of SNS impulse frequency, ganglion transmission, postganglionic nerve terminal, endorgan reactivity and baroreflex which might account for hypertension expressed in mature WKY-SHR.